I've always had trouble getting mens trousers/jeans, even pre HRT - my butt always stuck out because of my spinal curvature *lol* My waist-hip ratio was a bit whacky for a male as well which didn't help things either.
I found that when it came to buying jeans they'd either fit well in the seat and I'd have a large amount of material to cinch at the waist, or vice versa - which is probably similar to what a lot of you guys are dealing with. (Ironically, women's jeans have generally always fit me better - I got away with boot-cut ones, even though I didn't have much in the way of hips pre HRT).
What I did was buy jeans that fit around the hips/seat comfortably, cinch at the waist a bit, and then wear a t-shirt that was baggy/long enough to drape over my buttocks (generally half way). For you guys though, you'll still probably need to lose some weight and wait for some fat redistribution, and then also bulk up the upper body - if there's sufficient upper body bulk, then the loose fitting top will drape over the small waist and hide it. A bit of work involved and it's a sloppy sort of look.